Fluid-pressure controlled operating mechanism for a circuit breaker



Feb. 17, 1959 D. R. KURTZ SUR FLUID-PRES E CONTROLLED OPERATINGMECHANISM FOR A CIRCUIT BREAKER Filed Hay 23. 1957 Inventor: Donald R.Kurtz His ttorneg.

United States Patent Otiice 2,874,242 Patented Feb. 17, 1959FLUID-PRESSURE CONTROLLED OPERATING MECHANISM FOR A CIRCUIT BREAKERDonald R.. Kurtz, Drexel Hill, Pa., assignor to General ElectricCompany, a corporation of New York Application May 23, 1957, Serial No.661,126

8 Claims. (Cl. 200-82) This invention relates to a duid-pressurecontrolled operating mechanism for an electric circuit breaker, and moreparticularly, to improvements in the general type of operating mechanismshown and claimed in U. S. Patent No. 2,783,338, issued to I. W. Beattyand assigned to the assignee of the present invention.

In an operating mechanism of the type shown in the Beatty patent, thecircuit breaker contacts are held in the1r fully-open position by fluidpressure forces derived from pressurized gas trapped in a cylinder spaceat one side of a contact-controlling piston. A contact-closing operationis produced by venting gas from this cylinder space through a suitablebleed passage so as to reduce the liuid pressure forces tending to holdthe contacts open, thus allowing suitable biasing means to force thecontacts closed.

If the aforementioned bleed passage is relatively restricted, there area number of problems which tend to arise. First, there is the problemthat insufticient closing force will be available to overcome the highopposing forces which are abruptly established near the end of theclosing stroke if and when the breaker is closed on a fault. Second,there is the problem that the gas ahead of the contact-controllingpiston will still be pressurized, to some extent, when the contactsreach their fully-closed position. If the breaker is required toimmediately reopen (say, due to a fault on the power line), thencontactopening pressure will be built up from an initial pressureappreciably above atmospheric. In contrast, if the opening operationtakes place after the breaker has been closed for an extended interval,as would be the ordinary case, then opening pressure will be built upfrom an initial pressure equal to atmospheric. Since the opening-speedcharacteristics depend upon the initial pressure which is present,consistent characteristics would not be present for all openingoperations. Undesirable variations depending upon how long the breakerhad been closed would be present.

One way of overcoming these two problems is to form the aforementionedbleed passage of a relatively large size so that it is capable ofdumping air from the cylinder space at a very high rate. This approachis disadvantageous, however, in that it tends to result in unduly highcontact-closing speeds which could cause damage to the contacts.

An object of my invention is to provide, in a circuitbreaker of theabove type, a novel control arrangement which enables the contacts to beclosed at moderate speeds but yet enables the mechanism to overcome theopposing forces which are abruptly established near the end of theclosing stroke.

Another object is to provide an improved duid-pressure controlledoperating mechanism of the above type which has consistent opening-speedcharacteristics irrespective of the length of time the breaker has beenclosed when opening is initiated.

In carrying out my invention in one form, there is provided a circuitbreaker vwhich has a movable contact operatively connected to acontact-controlling piston. A supply of pressurized gas is maintained atone side of the piston in order to hold the contact in open position.Contact-closing is produced by venting this pressurized gas toatmosphere through a suitable bleed passage, thus allowing suitablebiasing means to force the contact into closed position. An additionalpassage which extends from said one side of the piston to the other issealed olf during initial contact-closing but is suddenly opened nearthe end of the closing stroke. This abruptly reduces the pressure of thegas -ahead of the piston and also tends to momentarily build up pressurebehind the piston. Such action makes available added force for finalcontact-closing and also helps to insure that the pressure in thecontact-opening chamber ahead of the piston will have been reduced toatmospheric by thel time a subsequent opening operation is initiated.

For a better understanding of my invention reference may be had to theaccompanying drawings, wherein:

Fig. l is a partially schematic sectional view of a circuit-interrupterembodying my invention. The interrupter is shown in the contact-closedposition.

Fig. 2 is a view similar to that of Fig. l but with the interrupter inthe contact-fully-open position.

Referring now to Fig. l, there is shown a circuit breaker of thesustained-pressure gas-blast type comprising an interrupting unitgenerally indicated at 10. This interrupting unit comprises an enclosedinterrupting chamber 11 deiined, in part, by a spherical metallic casing12 which is iilled with pressurized arc-extinguishing gas.

A pair of elongated conductive studs 15 and 20 project into the casing12 from diametrically-opposed points and each of these studs carries asuitable stationary contact assembly 16 at its radially-inner end.Cooperating with each stationary contact assembly is a movable contact28 pivotally mounted upon a stationary pivot 29. These pivots 29 aresupported on stationary brackets 31 which are integral with one end of astationary cylinder 32. Suitable means (not shown) are provided fortransferring current between the movable contacts and the brackets 31,so that the brackets 31 together with the cylinder 32 form a conductivepath electrically interconnecting the two movable contacts 28.

The cylinder 32, at its left hand end, is suitably supported from agenerally cylindrical housing 33. The housing 33, at its left hand end,has an annular `iiange 34 which is suitably bolted (by means not shown)against a mating flange 35 rigidly carried by the metallic casing 12.

For producing a gas-blast action for extinguishing the arcs which areestablished by separation of the contacts (as will soon be described),the housing 33 is prov1ded with a normally-closed annular exhaustpassage 36 which leads from the interrupting chamber 11 to thesurrounding atmosphere. The housing 33 at its right hand end is formedwith a pair of generally diametrically-opposed nozzle-type electrodes 38defining inlets to the exhaust passage 36.

For controlling the fiow of arc-extinguishing gas through the nozzleelectrode 38 and through the exhaust passage 36, there is provided atthe outer end of the exhaust passage 36 a cylindrically-shapedreciprocable blast valve member 40 which slides smoothly in asurrounding tubular Valve housing 41 integrally formed in the housing33. In Fig. l, the valve member 40 1s shown in its closed positionwherein an annular flange 42 formed at its left hand end sealingly abutsagainst the stationary ange 34, which serves as a valve seat. The valvemember 40 is normally maintained in this closed position of Fig. l bythe action of a suitable compression spring 44 and by the action of thepressurized gas within the passageway 36. This gas produces upon theflange 42 an unbalanced force urging the valve member 40 to the leftinto its closed position.

Since the chamber 11 is normally filled with pressurized gas, it will beapparent that when the valve member 40 is opened by movement tothe right(by means soon to be described), gas in the chamber 11 will ow at highspeed through the nozzles 38 andout the passage 36' past valve member 40to atmosphere, as is indicated by the arrows shown in Fig. 1. This rapidow of gas through the nozzles 38 creates lan axial arce'nv'eloping blastwhich acts rapidly to extinguish the arcs which are drawn adjacent thenozzles by movement of the movable contacts 28 away from their xedfingers 25.

For operating the blast valve 40 and the movable contacts 28, a combinedoperatingrnechanism 56 is provided. This mechanism 50 comprises 'twocooperating pistons 51 and 52 mounted for reciprocation in the cylinder32. The piston 51 is connected to the blast valve member 4t) by means ofa piston rod 54 which is shown extending through a central opening inthe valve member 40. This piston rod 54 has suitable threads formed'atits outer end for receiving a retaining nut 55 which clamps the valvemember 4Gy against a shoulder 56 formed on the piston rod 54. The pistonrod 54 also extends, in slidable relationship, through a central openingin a stationary end wall 57 provided for the cylinder 32. Al suitableseal 57 mounted in this end wall 57 lencircles the piston rod 54 andpre- Y vents gas from leaking around the piston rod.

The other piston 52 serves to control the movable contacts 28 and iscoupled to these contacts 28 by means of a piston rod S, a crosshead 59of suitable insulating material, and two sets of connecting links 60.The crosshead 59 is rigidly secured to the piston rod 58 b y suitableclamping means, whereas the connecting links 60 are pivotally connectedat 61 and 62 to the crosshead and the movable contacts, respectively.

In the position of Fig. 1, the movable contacts 28 are biased intoclosed position by means of overcenter compression springs 64. Each kofthese springs 64 has one end pivotally supported at 65 on a projectingportion of one of the brackets 31. At their inner ends, the springs 64are pivotallysupported on the crosshead 59. These overcenter springs 64tend to urge the contacts closed while the crosshead 59 is to the leftof a reference line connecting the pivots 65. But when the crosshead ismoved to the right beyond this reference line (as occurs during acontact-opening operation), the overcenter springs thereupon tend tourge the contacts in a contact-opening direction.

lThe contact-controlling piston 52 is formed Vwith a skirt portion 66,which in Fig. 1, is shown abutting the valve-controlling piston 51 andforming a space or chamber 67 between the two pistons. The skirt 66 isprovided with a series of notches, or recesses, forming radial ports 68extending through the skirt and into communication with the chamber 67.A circumferential bevelled groove 69 formed in the external wall of theAskirt 66 assures communication between these radial ports external ofthe skirt 66. The purpose of this chamber 67 and the radial ports 68will soon appear morerclearly.

Operation of the pistons 51 and 52 is initiated by supplying pressurizedgas to a small clearance space 70 located at the left hand end ofcylinder 32. Normally, this clearance space 70 is vented to atmosphereby means of a two-position control valve 71 which is mounted adjacent aduct 72 which leads into the clearance space 70. The control valve 71comprises a casing 73 having two radial ports 74 and 75, the first ofwhich 74 communicates with the surrounding atmosphere throughY asuitable exhaust duct '76 and the other of which 75 directlycommunicates with the pressurized gas inthe chamber 11. Flow throughthese ports 74 v 4 and is controlled by means of a reciprocable valveelement 77, which is releasably held in the elevated position shown inFig. 1. In this elevated position, a passageway 78 extending through thevalve element 77 affords communication between the lead-in duct 72 andthe exhaust duct 76, whereas the port 75 is sealed off by the valveelement 77. As a result, when the control valve element 77 occupies theposition of Fig. l, the clearance space 70 is vented to atmosphere andis sealed olf from the chamber 11.

In order to supply pressurized gas to the clearance space 70, it isnecessary to move the valve element 77 downwardly to seal off the ventport 74 and to establish communication between the inlet port 75 and thelead-in duct 72. This downward movement of valve element 77 can beinitiated either manually 0r in response to predetermined electricalconditions, e. g., a fault on the power circuit controlled by thebreaker. Any suitablemeans can be used for this purpose, and an exampleof such means is shown in the aforementioned Beatty patent. v

u When the control valve element 77 reaches the lower position, which isshown in Fig. 2, compressed gas ows from the chamber 11 through the port75 and the lead-in passage 72-into the clearance space 70. Pressure inthe clearance space quickly builds up and drives the `piston 5I rapidlyto the right. Since the contact-controlling piston 52 is then abuttingthe piston 51, it too is driven rapidly to the right. This movement tothe right takes place against the bias of closing springs 64 and alsoagainst the opposition of iluid contained within a-dash pot cylinder112V at the right of contact piston 52, as will be explained in greaterdetail hereinafter. The spiace 89 yimmediately to the right of piston 52is always freelyvvented to atmosphere through the duct 108, sorelatively little opposition is encountered fromsluid in this space.This movement of the piston 51 to the right immediately opens the blastvalve member 40, whereas thismmovement of piston 52 to the rightimmediately initiates opening movement of the contacts 28. The positionof the pistons 51 and 52 after this movement to the right is shown inFig. 2, with the valve-controlling piston shown in dotted lines. y

As soon as extinction of the arc is assured, the blast valve member 40is quickly returned to its closed position shown in Fig. l to preventfurther consumption of the compressed gas. To this end, a by-passpassage is provided which extends from the left-hand end of the cylinder32 to a preselected intermediate point in the bore of the cylinder. Whenthe pistons 51 and 52 occupy the position of Fig. l, the skirt portion66 of pistoiiSZ covers and closes off the by-,pass passage 85.` Theinterpiston chamber 67 is then at atmospheric pressure due tocommunication through a one-way valve 92 to atmosphere via duct 72, andalso due to the presence of a passage 200 (soon to be described).Whenthe two pistons 51 and 52 are moved simultaneously to the rightVfrom the position of Fig. l, as above-described, the by-pass 85 remainscovered until the peripheral groove 69 is moved into registry with themouth, or port, of the "by-pass. At this instant, which is illustratedby the dotted lines of Fig. 2, compressed gas flows from the by-pass 85through the groove 69 and the radial ports 68 into the chamber 67. As aresult, the fluid pressure within the chamber 67 quickly Vbuilds up tosubstantially the same value as the pressure at the left hand side ofpiston 51. Because that working surface of piston51 which is `exposed topressurized Huid within the chamber 67 is substantially larger than thatworking surface which is exposed to pressure tending to open the valve,thepiston 51 is subjected to an unbalanced 'force which quickly drivesthe piston 51, together with valve member 41), back into the closedposition shown by solid lines in Fig. 2, asis desired. During thisreturn movement, the fluid at the left hand side of the piston 51 isexpelled either throughl asma-12 the by-pass passage 85 or through theport 75 leading to the main chamber 11. The mouth of the by-pass 85 issolocated along the length of the cylinder wall that the blast valvemember 40 is returned to closed position only after the pistons 51 and52 have moved suiciently to assure that the arc drawn by separation ofthe contacts will have been extinguished.

The admission of fluid into the inter-piston chamber 67, in addition toclosing the valve member 40 as abovedescribed, also tends to hold themovable contacts 28 in open position. More particularly, so long as thecontrol valve element 77 remains in its lower position shown in Fig. 2,the pressure in the space between the two pistons corresponds to that ofthe chamber 11 and provides a force tending to hold the piston 52 in itsopen circuit position of Fig. 2. This force together with the action ofthe overcenter springs 64 is effective to maintain the contacts 28 inopen position, as will soon appear more clearly. During thisbreaker-open interval, the high internal pressure within the chamber 11provides adequate high dielectric insulation for the relatively shortisolating gap which now is maintained between the spaced contacts orelectrodes.

The speed at which the two pistons 51 and 52 move to the right duringthe above-described opening operation is controlled by dashpot meansforming a part of the operating mechanism. This dashpot means comprisesan auxiliary piston structure 110 which is slidably mounted within atubular `extension 112 of the main cylinder 32 located at the right handend of the main cylinder 32. The tubular extension 112 is provided withan outer end wall 118 containing metering passage 119 and a centralopening through which the piston rod 58 extends in slidablerelationship. The piston rod 5S contains keyway p orts 122 which permitfluid to ow through the central opening in the end wall 48 when thepiston rod 58 is in or adjacent the closed circuit position of Fig. 1.

The dashpot means allows initial opening movement of the pistons 51 and52 to take place at relatively high speed since the keyway ports 122 arethen open and air ahead of the piston can i'low freely therethrough.After a predetermined portion of the opening stroke has been completed,the piston rod 58 has moved suiciently to the-right to render the keywayports 122 no longer effective to vent air ahead of the piston 110.Thereafter, air can iiow only through the restricted passage 119, and asa result, there is established at the end of the opening stroke aretarding action which smoothly decelerates the pistons and contacts.

As explained hereinabove, the movable contacts 28 are held in theiropen-circuit position by iluid pressure maintained between the twopistons 51 and 52 and also by the action of the overcenter springs 64.These two forces which tend to hold the contacts open are opposed by thefluid pressure forces exerted on the auxiliary piston structure 110.This piston structure 110 is always acted upon iby a pneumatic forcefrom the right which tends to close the contacts and which variesdirectly in accordance with the uid pressure of the insulating gas inthe surrounding interrupter.

Assume now that the circuit breaker is in its fully open position, i.e., with the pistons 51 and 52 occupying their position of Fig. 2, andthat it is desired to close (or reclose) the breaker. This can beaccomplished simply by lifting the control valve element 77 from itslower vposition of Fig. 2 into its elevated position, therebyestablishing communication between the exhaust port 74 and the lead-inpassage 72 so as to vent the lead-in passage 72 to atmosphere. As aresult, pressurized iiuid is vented to atmosphere from the inter-pistonspace 67, through the check valve 92, the clearance space 70, and thelead-in passage 72. In response to such venting, the iiuid pressureforces exerted on the auxiliary piston structure 110 become operative todrive the pistons 52 and 110 to the left and to carry these pistons,together with the contacts 28, into their respective closed-circuitpositions. The overcenter springs 64 resist initial displacement ofthese parts from their respective open-circuit positions, but if the uidpressure within the interrupter is above a predetermined safe level, thepressure forces on the auxiliary piston predominate and overcome theresistance of the overcenter springs. Once the contacts 28 are movedbeyond dead center, the springs 64 would, of course, aid thiscontact-closing action and apply a desirable added closing force as thecontacts approached engagement. The keyway ports 122 also contribute toincreased closing force near the end of the stroke by permitting acomparatively free iniiux of air into the tubular extension 112 near theend of the stroke.

The above-described lifting of the control valve element 77 to effectclosing of the breaker can be accomplished in any suitable manner, as bymeans of a solenoid arrangement shown inthe aforementioned Beattypatent.

In connection with the above-described closing action, I prefer to makethe valve 92 and the passageways 76 and 78 of relatively small size sothat air from the interpiston space 67 is vented at a relativelymoderate speed, which allows the air within the chamber 67 to exert anappreciable retarding action on the piston 52 during initialcontact-closing.

If these vent passages were of a relatively large size and thereforevented the interpiston space 67 at an appreciably greater speed, thenobjectionably high contactclosing speeds would be obtained. In thisregard, excessively high closing speeds can damage the breaker contactsdue to high velocity impacts.

If the above-described closing action took place when there was a fault,or short-circuit, present on the power circuit in question, then as soonas current began t0 ow between the contacts, very high opposing forcesof a well-known character would be abruptly established.

For overcoming these opposing forces, I provide a passageway 200 whichextends through the contact-controlling piston 52 between its oppositesides. In the closed-circuit position shown in Fig. l this passageway200 alords free communication between the inter-piston space 67 and thecylinder space 89 behind the piston 52.

As will be apparent from the drawings, the mouth 201 of the passageway200 is located in the axially-projecting rod portion 202 of the piston52. When the breaker is in the fully-open position of Fig. 2, the rodportion 202 is disposed within the tubular extension 112 of the cylinder32. Because this tubular extension closely surrounds the rod portion 202in the position of Fig. 2, it covers the mouth 201 and therefore acts toseal ofr the passageway 200. When the piston 52 is driven to the lefttoward the closed-circuit position, as described hereinabove, thepassageway 200 remains sealed off by the tubular extension 112 duringthe initial portion of the closing stroke. However, just before thepiston 52 reaches a point at which current iiows between the thenclosingcontacts, the mouth 201 moves out of the tubular extension 112 therebyallowing free communication to be established between the inter-pistonspace 67 and the cylinder space 89 at the rear of the piston 52. Thisabruptly reduces the pressure in the inter-piston space 67 and alsomomentarily increases the pressure in the space 89 behind the piston 52.As a result of the abrupt drop in pressure on the front side of thepiston 52, the uid pressure forces opposing closing-motion of the piston52 areabruptly reduced; and as a result of the momentary increase inpressure on the rear side of the piston 52, additional huid-pressureforces are temporarily available to aid in closing the contacts. Each ofthese factors, especially the rst, materially aids the mechanism toovercome any short-circuit-produced opposing forces which might beencountered at the end of the closing stroke.

Another important function of the passageway 200 is that it insuresconsistent opening-operation characteristics irrespective of whether thebreaker vis opened immediately after closing or a considerable length oftime after closing, as would be the ordinary case. In this regard,assume rst that the passageway 200 was not present and that air was bledthrough the exhaust passages 76, 78, during closing, at thecomparatively moderate rate described above. Under such circumstances,due to the restricted venting, there is a delinite tendency for thepressure within the chamber 7() to be above atmospheric immediatelyafter the breaker is fully-closed. If a subsequent opening operationimmediately followed, then pressure in the contact-opening chamber 70would build up from an initial pressure higher than atmospheric. This isin contrast to any ordinary opening operation, in. which such pressurebuilds up from an initial pressure equal to atmospheric. Thus, withoutthe passageway 200, diiierent opening-speed characteristics would beobtained, depending upon the length of time the breaker remained closed.

The presence of the passageway 2Gb, however, overcomes this problembecause it provides a parallel venting path Vwith respect to that pathextending through the valves 92 and 77. As a result, much less air isrequired to ow through the latter venting path, thus minimizing thelikelihood that the pressure in the chamber 70 will be above atmosphericat the time the breaker reaches its fully-closed position.

f. The air which flows into chamber 89 from the interplston space 67brieliy provides added closing force on the piston 52, as describedhereinabove, but quickly falls to atmospheric (due to the bleed passage108) in time to avoid interference with a subsequent opening operation.

Because of its particular location, the passageway 200 1n no wayinterferes with a normal opening operation. In this regard, duringinitial opening movement, the bypass 85 is sealed oil" by the skirtportion 66 of the piston 52, thus preventing pressurized air from owingthrough the passsageway 200 to the chamber 89 at the rear of the piston.Before the bypass 85 is uncovered near the end of the opening stroke,the mouth 201 of passageway 200 is covered by the internal wall oftubular extension 112. This closes off the passageway 200 and, thus,when the bypass 85 is opened lnear the end of the opening stroke,pressurized air `still is unable to ow through the passageway 200 to thechamber '89 at the rear of the piston. Thus, since pressurized air isblocked from flowing through the passageway 200 during the entireopening operation, its presence in no way interferes with the openingoperation. l

.Another important advantage of locating the passageway 200 in theparticular position shown is that a very effective seal can be readilyprovided to preventl leakage through the passageway 200 to atmosphereduring the time the breaker remains in the fully-open position. In thisregard, when the breaker is in the fully open position of Fig. 2,leakage of pressurized gas through the passageway 200, about the rodportion 202 to the atmospheric chamber 89 is positively prevented by aresilient seal 210 provided between the piston 52 and the end wall 212of the cylinder 32. This resilient seal 210, which is preferably carriedin an annular groove in the piston 52, is compressed between the piston52 and the end wall 212 when the breaker is in the fully-open positionof Fig. 2 by those forces tending to normally hold the contacts in openposition. y

The internal wall of the tubular extension 112 is capable of sealing thepassageway 200 suiciently to prevent the ow of any appreciable amount ofair through the passageway on a short time basis (say, during abreaker-operation). But this sealing action is not adequate to preventappreciable air leakage on along time basis (say, for the extended'periods duringv which the breaker might remain in open position).During such intervals, the resilient seal 210 is effective to preventleakage to atmosphere.

When the breaker is in the closed position of Fig. l, an O-ring 214prevents any air from leaking about the rod portion 202 to theatmospheric chamber l89.

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that variouschanges and modications may be made without departing from my inventionin its broader aspects and I, therefore, intend in the appended claimsto cover all such changes and modiiications as fall within the truespirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is: l

l. In an electric circuit breaker comprising a contact movable betweenspaced-apart open and closed position, biasing means urging said contacttoward closed position, a movable piston operatively connected to saidcontact and also urged toward a closed position by said biasing means,means for maintaining a supplyof pressurized gas on one side of saidpiston for holding said contact in open position in opposition to saidbiasing means, means for bleeding pressurized gas from said one side ofthe piston to allow said biasing means to drive said contact and saidpiston toward closed position, a passageway leading from said one sideof the piston to the other side thereof, and means for sealing oli saidpassageway during initial contact-closing movement and for opening saidpassageway during nal contact-closing movement, said passageway openingoccurring prior to the point at which said contact reaches closedposition and acting to abruptly reduce the forces opposing finalcontact-closing movement.

2. vIn an electric circuit breaker comprising a contact movable betweenspaced-apartV open and closed positions, biasing means urging saidcontact toward closed position, a movable piston operatively connectedto said contact and also urged toward a closed-contact position by saidbiasing means, contact-opening means for driving said piston from saidclosed-contact to an open-contact position to produce opening of saidcontact, means for maintaininga supply of pressurized gas on one side ofsaid piston for holding said contact in open position in opposition tosaid biasing means, means for bleeding pressurized gas from said oneside of the piston to allow said biasing means to drive said Contact andsaid piston toward closed position, a passageway leading from said oneside of the piston to the other side thereof, and means for sealing ottsaid passageway during initial contact-closing movement and for openingsaid passageway during final contact-closing movement, said passagewayopening occurring prior to the point at which said contact reachesclosed position and acting to abruptly reduce the Vforces opposing nalcontact-closing movement. i 3. In an electric circuit breaker comprisinga contact movable between spaced-apart open and closed positions, amovable piston operatively connected to said contact and movable from acontact-open to a contactclosed position during a contact-closingstroke, biasing means urging said contact and said piston toward theirrespective closed positions, said piston having a rod portion projectingaxially from one side thereof, cylinder means slidably receiving saidpiston and having a tubular portion projecting from an end wall thereoffor slidably receiving said rod portion, means for maintaining a supplyof pressurized gas on the other side of said piston for holding lsaidcontact in open position in opposition to said biasing means, means forbleeding pressurized gas from said other side of the piston to allowsaid biasing, means to drive said contact toward closed position, apassageway `extending through said piston and terminating in a mouthwhich is located in said rod portion, .said mouth being so located thatit is sealed off by said tubular portion when said piston is in theregion of contact-open position and communicates freely with thecylinder space at said one side of the piston when the piston nears itsclosed-contact position, said free communication being establishedduring a closing operation prior to the point at which said contactreaches closed position.

4. In combination with the circuit breaker of claim 3, resilient sealingmeans located between said one side of the piston and said cylinder endwall for preventing leakage of pressurized gas through said passagewayand about said rod portion when said piston is in the contactopenposition.

5. In an electric circuit breaker comprising a contact movable betweenspaced-apart open and closed positions, biasing means urging saidcontact toward closed position, a movable piston operatively connectedto said contact and also urged toward closed position by said biasingmeans, said piston having one side thereof vented to a region ofrelatively low pressure, means for maintaining a supply of pressurizedgas on the other side of said piston for holding said contact in openposition in opposition to said biasing means, means including a bleedpassage for venting pressurized gas from said other side of the pistonto allow said biasing means to drive said contact toward closedposition, a second passageway extending through said piston to aiordcommunication between opposite sides thereof, and means for sealing ott'said second passageway during initial contact-closing movement and foropening said passageway during nal contact-closing movement saidpassageway opening occurring prior to the point at which said contactreaches closed position and acting to abruptly reduce the forcesopposing nal contact closing movement.

6. In an electric circuit breaker comprising a contact movable betweenspaced-apart open and closed positions, biasing means urging saidcontact toward closed position, a movable piston operatively connectedto said contact and also urged toward a closed-contact position by saidbiasing means, cylinder means slidably receiving said piston anddeiining a contact-opening chamber at one side of said piston, meansresponsive to the admission of pressurized gas to said contact-openingchamber for driving said piston from said closed-contact to anopencontact position to produce opening of said contact, means formaintaining a supply of pressurized gas on one side of said piston forholding said contact in open position in opposition to said biasingmeans, means including a bleed passage extending from said one side 10movable between spaced-apart open and closed positions, biasing meansurging said contact toward closed position, a movable piston operativelyconnected to said contact and also urged toward a closed-contactposition by said biasing means, cylinder means slidably receiving saidpiston and dening a contact-opening chamber at one side of said pistonfor receiving pressurized gas which acts to drive said piston from saidclosed-contact to a contact-open position to produce opening of saidcontact, means for maintaining a supply of pressurized gas on one sideof said piston for holding said contact in open position in oppositionto said biasing means, closing-control means including a bleed passagewhich upon opening acts to vent said contact-opening chamber.

and to allow said biasing means to drive said Contact toward closedposition, a second passageway leading from said one side of the pistonto the other side thereof, and means for sealing off said secondpassageway during initial contact-closing movement and for opening saidsecond passageway during final contact-closing movement, saidpassageway-opening occurring prior to the point at which said contactreaches closed position and acting to abruptly reduce the forcesopposing final-closing movement.

8. In an electric circuit breaker comprising a contact movable betweenopen and closed positions, a movable piston operatively connected tosaid contact and movable between a contact closed position and a contactopen position during contact opening, contact-opening means for drivingsaid piston from said contact-closed position to said contact-openposition to produce opening of said movable contact, a first passagewayadapted when open to supply pressurized gas to a space at one side ofsaid piston whereby to hold said contact in open position, means actingto close olf said first passageway during initial contact-opening and toopen said passageway during tnal contact-opening, a second passagewayaffording communication between opposite sides of said piston when thepiston is in the region of its closed position, means for sealing oisaid second passageway at an intermediate point in the opening strokeprior to the point at which said first passageway is opened, and meansfor initiating contact-closing in response to venting of said space atsaid one side of the piston, said sealing means acting to seal ott saidsecond passageway during initial contact-closing but allowing gas to Howtherethrough during nal contact-closing from a time just prior to thepoint at which said contact reaches closed position.

References Cited in the tile of this patent UNITED STATES PATENTS2,578,349 Goodwin Dec. l1, 1951 2,730,588 Kelle Jan. 10, 1956 2,736,295Peek Feb. 28, 1956 2,783,338 Beatty Feb. 26, 1957 FOREIGN PATENTS122,860 Austria May 26, 1931

